Unennbium
Unennbium, Ueb, is the temporary name for element 192. NUCLEAR What follows is based on a first-order, liquid-drop assessment of where the outer boundary of the nuclear world is. Assume cautious values for how many neutrons a nucleus with 192 protons can bind (high neutron dripline) and how few it can have before it fissions immediately regardless of how much the structure it can develop stabilizes it (low must-fission curve). Assume, too, that anything that lasts long enough so that protons and neutrons can be treated as particles rather than collections of quarks (is causal) might be a nucleus. Under these conditions, Ueb isotopes are theoretically possible between Ueb 505 and Ueb 844 (see "The Final Element", this wiki). Ueb 505 through Ueb 673 are expected to decay by beta emission if they don’t fission quickly. Above that value of A, the confident neutron dripline, drops may decay by neutron emission before they can fission. (Structural correction does not affect neutron emission.) Isotopes lighter than Ueb 531 need more than twice the structural correction energy needed to prevent fission in worst-case nuclei in the A = 480 region(1). Predicting whether or not the structure a nuclear drop can develop will allow it to survive for the 10^-14 sec required for it to bind an electron and so become an atomic nucleus is not usually possible at this time. Neutron shell closures have been predicted at N = 524, 406, and 370(2),(3),(4). The isotope Ueb 716 is 6% above the confident dripline, which means isotopes stabilized by the N = 524 closure are likely to decay by neutron emission. The isotope Ueb 598 requires 7.5 MeV of structural correction, which means some isotopes in the Ueb 588 to Ueb 603 band are likely, if the N = 406 closure is strong. Long beta-decay half-lives are possible at Ueb 590 and below, which may allow decay by alpha emission in the bottom portion of the band. Ueb 562 requires 15.5 MeV of structural correction energy, which means it is unlikely to stabilize any isotopes of Ueb. Isotopes between Ueb 531 and Ueb 747 have some probability of existing. Outside this band, isotopes of Ueb are nearly impossible. ATOMIC Electron structure of Ueb has not been studied closely, but it is likely to differ significantly from the conventional orbitals found in lower-Z nuclei. While only the innermost electrons would be qualitatively different, other electrons are likely to be quantitatively different from those in lower-Z atoms. Ueb is also large enough that nuclear shape may have an effect on electron structure, which might cause different isotopes of Ueb to have different electronic structures. (That means it is no longer an element in the chemical sense.) Predictions of atomic or chemical properties of Ueb are risky. FORMATION Ions of this element may form when material from roughly 1 km depth is ejected from a disintegrating neutron star during a merger. It is probably impossible for lighter isotopes to form in this way. Fusion or multinucleon transfer reactions in the polar jets emanating from a neutron star or black hole might produce lighter isotopes, including those in the Ueb 588 to Ueb 603 band. Quantities amount to a few atoms per star at best. REFERENCES 1. "Decay Modes and a Limit of Existence of Nuclei"; H. Koura; 4th Int. Conf. on the Chemistry and Physics of Transactinide Elements; Sept. 2011. 2. "Magic Numbers of Ultraheavy Nuclei"; V. Yu Denisov; Physics of Atomic Nuclei, v. 68, no. 7, pp 1133-1137; 2005. 3. “Search for Superheavy Elements Among Fossil Fission Tracks in Zircon”; J. Maly & D.R. Walz; Stanford Linear Accelerator Center publication SLAC-PUB-2554; July 1980. 4. “Single Particle Levels of Spherical Nuclei in the Superheavy and Extremely Superheavy Mass Region”; H. Koura and S. Chiba; Journal of the Physical Society of Japan; DOI 10.7566/JPSJ.82.014201; Jan. 2013. (12-07-19)